Data from field and laboratory studies suggest that primate social structure is based on differential responding to conspecifics, to particular categories of social partners within conspecific groups, and to particular individuals within these categories. The long- range goal of the present research is to specify the social/experiential and perceptual/cognitive factors that contribute to the development of social perception in the primate infant. Various laboratory experimental techniques are used to provide systematic quantitative assessment of visual aspects of social perception in adult pigtailed macaque (Macaca nemestrina) subjects. The specific objectives of the research are (1) to determine the types of social category distinctions made by adult socially-reared macaques, and (2) to determine the contribution of cognitive processes such as memory and attention to social perception in macaques. It is expected that the results of the proposed studies, taken as a whole, will provide an empirical framework for the development of a theoretical approach to primate social perception, as well as an empirical foundation for future studies of the developmental determinants of primate social perception.